Guide Assembly for a Disc Brake

ABSTRACT

A guide assembly for a disc brake, the guide assembly comprising a bore disposed in a disc brake caliper for receiving a guide pin. The bore comprises a first bore portion with a substantially circular cross-sectional profile and a second bore portion with a substantially circular cross-sectional profile arranged sequentially along the length of the bore and tangentially offset such that the bore is defined by the overlap of the first bore portion and second bore portion and has a lens-shaped cross-sectional profile.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 14/643,174,filed Mar. 10, 2015, the disclosure of which is hereby incorporated inits entirety by reference herein.

TECHNICAL FIELD

The present invention relates to a disc brake and particularly but notexclusively to a guide assembly for slidably mounting a caliper of adisc brake.

BACKGROUND

Disc brakes are commonly used for braking heavy vehicles such as trucks,buses and coaches.

Disc brakes conventionally comprise a brake carrier and a caliper. Thebrake carrier is arranged to carry brake pads on each side of a rotor.The caliper is slidably mounted on the brake carrier by two or moreguide assemblies, such that when the disc brake is actuated, the caliperis able to slide with respect to the brake carrier so as urge the brakepads onto a rotor in a clamping action and thereby effect braking.

A guide assembly typically comprises a guide pin along which the calipercan slide and a bore disposed in the caliper for receiving the guidepin.

To achieve free sliding of the caliper in a broad range of operatingconditions, the guide assemblies must take account of manufacturingtolerances, effects of heating or cooling in use, and accommodatedeflections of the disc brake due to the braking torque.

Previously, it has been found that these constraints can be compensatedby inserting an oval, solid guide bush in the bore to guide the guidepin, the diameter of the oval being approximately 2 mm greater in thelateral direction where play is required than in the other,perpendicular direction. However, this solution is undesirable becausethe manufacture and insertion of oval, solid guide bushes (for example,by using a casting or sintering process) is complex, time consuming andexpensive.

SUMMARY

The present invention seeks to alleviate the problems associated withthe prior art.

Accordingly a first aspect of the invention provides a guide assemblyfor a disc brake, the guide assembly comprising: a bore disposed in adisc brake caliper for receiving a guide pin, wherein the bore comprisesa first bore portion with a substantially circular cross-sectionalprofile and a second bore portion with a substantially circularcross-sectional profile arranged sequentially along the length of thebore and tangentially offset such that the bore has a lens-shapedcross-sectional profile.

Due to the lens-shaped cross-sectional profile of the bore, clearancebetween the guide pin and the bore in the tangential direction Y isreduced or minimised and clearance between the guide pin and bore in thecircumferential direction X is increased or maximised. Accordingly, theundesirable effects of noise, stress and excess wear due to vibration ina tangential direction Y are restricted, whilst the manufacturingtolerances and deflections due to braking torque in a circumferentialdirection X are accommodated.

Providing a bore with a lens-shaped cross-sectional profileadvantageously avoids the need for an oval, solid bush to guide theguide pin. Moreover, the formation of a bore with a lens-shapedcross-sectional profile defined by the overlapping parts of sequentialand tangentially offset bore portions with substantially circularcross-sectional profiles is simpler, quicker and more cost-effectivethan the complex, time-consuming and expensive manufacturing of an oval,solid bush.

In an embodiment where the diameter of the first bore portion is D,length of the first bore portion is L1, the diameter of the second boreportion is D, the length of the second bore portion is L2 and thecentreline of the second bore portion is tangentially offset from thecentreline of the first bore portion by a predetermined distance O, thetangential diameter of the bore TD=D−O, the circumferential diameter ofthe bore RD=D and the length of the bore L=L1+L2.

The first bore portion and second bore portion may have substantiallythe same diameter and/or may be offset solely in the tangentialdirection.

The first bore portion and second bore portion may be offset by adistance of between 5-20%, preferably by a distance between 9-15% oreven more preferably by a distance of 12% of the average diameter of thefirst bore portion and second bore portion. Due to the lens-shapedcross-sectional profile of the bore, the clearance between the guide pinand the bore in the tangential direction Y may be a distance of between0.1-0.6 mm, or preferably by a distance of between 0.15-0.2 mm and theclearance between the guide pin and the bore in the circumferentialdirection X may be a distance of between 1-2 mm.

The first bore portion and second bore portion may be of substantiallyequal length.

At least one, but preferably both, of the first and second bore portionsmay further comprise a guide bush member mounted therein.

Due to the configuration of the bore portions, the guide bush membersalso have a sequential and tangentially offset arrangement such that theguide bush subsequently has a lens-shaped cross-sectional profile inoverlap.

Advantageously, forming a guide bush with an lens-shaped cross-sectionalprofile in overlap by inserting guide bush members with substantiallycircular cross-sectional profiles into sequential and tangentiallyoffset bore portions is a simpler process than the complex,time-consuming and expensive manufacturing of an oval, solid bush byprior art methods.

The guide assembly may further comprise a guide pin along which the discbrake caliper can slide relative to a carrier of the disc brake. Theguide pin may comprise a fastener for securing the guide pin to thecarrier of the disc brake and a sleeve having an outer guide surface.

A second aspect of the invention provides a disc brake calipercomprising a first bore for receiving a first guide pin, the borecomprising: a first bore portion having a substantially circularcross-sectional profile; and a second bore portion having asubstantially circular cross-sectional profile, whereby the first boreportion and second bore portion are arranged sequentially along the boreand tangentially offset such that the bore has a lens-shapedcross-sectional profile.

The disc brake caliper may comprise a guide bush located within thefirst bore. The guide bush may comprise: a first guide bush memberinserted in the first bush portion, having a substantially circularcross-sectional profile and forming a close fit with the first boreportion; and a second guide bush member inserted in the second bushportion, having a substantially circular cross-sectional profile andforming a close fit with the second bore portion.

The disc brake caliper may advantageously further comprise a secondbore, the second bore having a substantially circular cross-sectionalprofile. At least one bush member having a substantially circularcross-sectional profile may be located in the second bore. The bushmembers mounted within the first bore and second bore may besubstantially identical.

In a third aspect of the present invention, there is provided a discbrake comprising a disc brake caliper according to the second aspect ofthe present invention and a disc brake carrier, the disc brake carriercomprising a first guide pin arranged to be received in the first bore.

If the disc brake caliper further comprises the second bore, then thedisc brake carrier has a second guide pin arranged to be received in thesecond bore.

A fourth aspect of the present invention provides a method of forming abore in a disc brake caliper, the method comprising: machining from afirst side of the caliper to form a first bore portion with asubstantially circular cross-sectional profile; and machining from asecond side of the caliper to form a second bore portion with asubstantially circular cross-sectional profile that is sequential andtangentially offset from the first bore portion.

The method may further comprise inserting a first guide bush member witha substantially circular cross-sectional profile in the first boreportion and inserting a second guide bush member with a substantiallycircular cross-sectional profile in the second bore portion.

A further aspect of the invention provides a method of forming a bushfor receiving a guide pin, the method comprising: providing a strip ofmetal; broaching or otherwise machining two portions of the strip so asto thin those portions with respect to the remainder of the strip;forming the strip into a tube such that the two portions are on opposinginner faces of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is an isometric view of a disc brake having the guide assembly ofa first embodiment of the present invention and sectioned through theguide assembly;

FIG. 2 is an enlarged isometric cross-sectional view of the guideassembly shown in FIG. 1;

FIG. 3 shows a cross-sectional view of the bore of the guide assembly ofFIG. 1;

FIG. 4 shows schematically the cross-sectional profile of the bore ofthe guide assembly of FIG. 1 normal to the cross-section of FIG. 3;

FIG. 5 shows a perspective, cross-sectional view of guide assembly of asecond embodiment of the present invention;

FIG. 6 shows a cross-sectional view of the bore of the guide assembly ofFIG. 5;

FIG. 7 shows schematically a cross-sectional profile of the bush of theguide assembly of FIG. 5 normal to the cross-section of FIG. 6;

FIG. 8 shows a cross-sectional profile a bush of a guide assembly of athird embodiment of the present invention; and

FIG. 9 shows a perspective, cross-sectional view of the bush of FIG. 8.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

Referring to FIGS. 1 to 7, a guide assembly for a disc brake 8 accordingthe present invention is indicated generally at 10. The guide assemblyis provided in the disc brake 8 to slidably mount a caliper 20 of thedisc brake with respect to a brake carrier 30 of the disc brake.

In a first embodiment of the guide assembly 10 as shown in FIGS. 1 to 4,the guide assembly 10 comprises a guide pin 11 along which the caliper20 can slide and a bore 12 disposed in the caliper for receiving theguide pin.

The guide pin 11 comprises a fastener to secure the guide pin to thebrake carrier. In the first embodiment depicted in FIGS. 1 to 4, thefastener is a bolt 11 a that affixes to the brake carrier by screwinginto a threaded bore in the brake carrier 30.

With particular reference to FIG. 2, the guide pin 11 further comprisesa guide sleeve 11 b at least substantially surrounding the fasteningmeans and over which the caliper 20 slides. The sleeve is a hollow,thin-walled tube with a substantially circular cross-sectional profile.The outer surface of the sleeve may be coated with PTFE to aid thesliding action of the caliper along the guide pin.

When attached to the brake carrier 30, the guide pin 11 extends in anaxial direction A. Direction A is parallel to an axis R of rotation of arotor 40 (shown in part) of the disc brake 8 and parallel to thetransverse axis of the disc brake.

The bore 12 of the guide assembly 10 is an elongate hole extending froma first caliper side (inboard) 20 a to the second caliper side 20 b(outboard) of the caliper. The caliper 20 is slidably mounted withrespect to the brake carrier 30 by sliding the guide pin 11 through thebore 12. Hence, when the disc brake is actuated, the caliper 20 is ableto slide in the axial direction A along the guide pin 11.

The bore 12 comprises a first bore portion 12 a with a firstsubstantially circular cross-sectional profile and a second bore portion12 b with a second substantially circular cross-sectional profile. Thefirst bore portion 12 a and second bore portion 12 b are arrangedsequentially along the bore and offset in a tangential direction Y.Direction Y is tangential to a circle described by the rotation of therotor 40 of the disc brake 8, perpendicular to the axial direction A,perpendicular to the longitudinal axis of the disc brake and parallel tothe direction in which brake pads 50 a, 50 b are inserted or removedfrom the brake carrier 30.

Due to the sequential and tangentially offset arrangement of the firstbore portion and second bore portion the cross-sectional profiles ofeach of the bore portions intersect such that the bore subsequently hasa stepped longitudinal profile as shown in FIG. 3 and a quasi-ovalcross-sectional profile, where the two bore portions 12 a and 12 boverlap as shown in FIG. 4. The smallest cross-sectional dimension ofthe bore extends in the tangential direction Y. The largestcross-sectional dimension of the bore extends in a generallycircumferential direction X. Direction X is perpendicular to the axialdirection A, perpendicular to the tangential direction Y and parallel tothe longitudinal axis of the disc brake.

To allow the caliper to slide along the guide pin, the diameter of theguide pin 11 is selected to correspond approximately to the tangentialdiameter of the bore 12. Therefore, the clearance between the bore 12and the guide pin 11 in the tangential direction is minimised, vibrationis reduced and so the undesirable effects of noise, stress and excesswear are restricted. Whereas, the greater clearance provided between thebore and the guide pin in the circumferential direction X providessufficient lateral play to allow for manufacturing tolerances anddeflections of the brake carrier and guide pin due to the brakingtorque. In practice this results in the guide pin being in potentialsliding contact with the lower part of bore portion 12 a and the upperpart of bore portion 12 b only, because these are the surfaces that formthe lens-shaped profile.

The sequential and tangentially offset bore portions 12 a, 12 b can beformed by machining the first bore portion into the caliper from thefirst caliper side 20 a with a predetermined diameter and depth andmachining the second bore portion into the caliper from the secondcaliper side 20 b with a predetermined diameter, depth and offsetdisplacement until they intersect. Due to the circular cross-sectionalprofiles of the bore portions, the bore portions may be machined usingconventional drilling techniques. Hence, the bore 12 can be formedsimply, quickly and cost effectively. The bore may be treated or coatedafter machining in order to improve its wear performance.

The first bore portion and second bore portion may have differentdiameters or substantially the same diameter. The first bore portion andsecond bore portion may have different lengths or substantially the samelength. The first bore portion and second bore portion may be offsetsolely in the tangential direction Y.

In the first embodiment depicted in FIGS. 1 to 4, the first bore portion12 a has a cross-sectional circular profile with diameter D and lengthL1, the second bore portion has a cross-sectional circular profile withdiameter D and length L2 and the centreline C1 of the first bore portionis offset solely in the tangential direction to the centreline C2 of thesecond bore portion by displacement O. The centrelines C1 and C2 aresubstantially parallel. The resulting bore has a length L=L1+L2 and hasa quasi-oval, overlapping cross-sectional profile where the minimumdiameter in the tangential direction TD=D−O and the maximum diameter inthe circumferential direction RD=D.

In geometric terms, the overlap may be considered a symmetric lens,although given the limited offset with respect to the diameters of thebores, the shape 25 approximates sufficiently to an oval of the priorart bush to be functionally equivalent.

In addition to the features of the first embodiment of the guideassembly a second embodiment of the guide assembly as shown in FIGS. 5to 7 also includes a bush 13 to guide the guide pin within the bore.This arrangement is preferred as it improves the durability andserviceability of the guide assembly 10. The bush comprises a first bushmember 13 a and a second bush member 13 b. The first bush member 13 ahas a substantially circular cross-sectional profile that is configuredto form a close fit with the first bore portion 12 a and act as an innerliner in the first bore portion. Likewise, the second bush member 13 bhas a substantially circular cross-sectional profile that is configuredto form a close fit with the second bore portion 12 a and act as aninner liner in the second bore portion. For heavy vehicle applicationsthe internal diameter of the bush members are typically in a range of25-40 mm.

Due to the substantially circular profiles of the bore portions, theguide bush members may comprise solid sleeved, hollow tubular bushmembers having a substantially circular cross-sectional profile. Thebush members may be manufactured from steel, bronze, plastic, rubber ora composite of any of these, and may include a low friction coating suchas PTFE. The bushes may have a plain inner surface or a suitable patternof depressions to assist in the sliding of the caliper. In a preferredembodiment the bushes may be the same as the bushes used for a circularguide pin arrangement used at the circumferentially opposite side of thebrake caliper on the brake (see below).

Due to the sequential and offset arrangement of the bore portions 12 a,12 b, the cross-sectional profiles of the first bush member 13 a and thesecond bush member 13 b overlap such that the bush within the bore has astepped longitudinal profile (see FIG. 6) and an quasi-ovalcross-sectional profile (see FIG. 7).

The first bush member 13 a may be inserted into the first bore portion12 a from the first caliper side 20 a. The second bush member 13 b maybe inserted into the second bore portion 12 b from the second caliperside 20 b.

When a bush is provided in the bore, the diameter of the guide pin isselected to correspond to the smallest cross-sectional dimension of thebush overlap. Accordingly, the clearance gap between the guide pin andthe bush in the tangential direction Y is minimal and so vibration,noise, stress and excess wear are reduced. The largest cross-sectionaldimension of the bush provides a greater clearance gap between the guidepin and the bush in the circumferential direction X to allow for playdue to manufacturing tolerances, heat expansion and brake torque.

The embodiments of the guide assembly are suitable for use in any typeof disc brake, including pneumatic, hydraulic, electrically andmechanically actuated disc brakes. However, the embodiments are believedto be particularly beneficial in air-actuated disc brakes for heavycommercial vehicles, where rotors typically have a diameter of between30-60 cm, meaning that the torque and heat effects may be moresignificant than in hydraulic disc brakes for smaller, lighter vehicles.

FIG. 1 depicts an embodiment of a disc brake 8. The disc brake comprisesa caliper 20 slidably mounted with respect to a brake carrier 30 by twoguide pin assemblies. The caliper 20 has a housing typically formed fromcast iron or steel. The brake carrier 30 is typically also formed fromcast iron or steel.

The brake carrier 30 carries an inboard brake pad 50 a and an outboardbrake pad 50 b. A rotor 40, rotatable about an axis extending in theaxial direction A, is positioned between the brake pads. An air actuator(not shown) is provided to move the inboard brake pad 50 a intofrictional contact with the rotor. When the inboard brake pad 50 a ispushed towards and contacts the rotor, the caliper 20 slides inboardalong the guide pins of the guide pin assemblies. As the caliper slidesinboard it moves the outboard brake pad 50 b towards the rotor. Hence,the rotor 40 becomes clamped between the inboard and outboard brake padsand the rotation of the rotor is frictionally inhibited. So as toaccommodate installation and deflection constraints, the first guideassembly is a guide assembly 10 according to the first embodiment of theinvention in which the bore has a lens-shaped cross-sectional profile.The second guide assembly is a conventional guide assembly 6 comprisinga guide pin (not shown), a bore (not shown) with a circularcross-sectional profile to receive the guide pin and at least one guidebush member (not shown) with a circular cross-sectional profile to guidethe guide pin within the bore. These bushes may be the same as the firstand second bush members 13 a and 13 b, thereby minimising the number ofparts required to assemble and service the brake. The guide pin of thesecond guide assembly 6 is preferably longer than the guide pin of thefirst guide assembly 10 to provide a more positive attachment andguidance to the brake carrier and location for the caliper.

In an alternative embodiment of guide assembly, a conventionalcylindrical bore (not shown) may be formed in the caliper by a machiningoperation and at least one bush 113 shown in FIGS. 8 and 9 then insertedtherein. The bush is initially provided as a rectangular plate ofsuitable material (e.g., brass). The plate is thinned at predeterminedlocations 115 in a broaching or other suitable machining operation, andmay also have recesses 117 formed in a sliding surface 119 thereof. Theplate is then formed into the tubular bush illustrated in FIGS. 8 and 9such that the thinned locations are on opposing sides of an inner faceof the bush, and act in conjunction with a circular guide pin to providethe required amount of play in the X direction.

Advantageously, the guide pin receiving bore with a lens-shapedcross-sectional profile allows for free sliding of a guide pin andeliminates the need for an oval bush formed by a costly process, such assintering. The manufacture of the guide pin receiving bore with thelens-shaped cross-sectional profile in overlap can be achieved in asimple and cost effective manner. In addition, the construction andinsertion of guide bush members in a guide pin receiving bore havingsequential and tangentially offset bore portions so as to provide aguide bush within the guide pin receiving bore with the lens-shapedcross-sectional profile is straightforward and inexpensive.

Although the invention has been described above with reference to one ormore preferred embodiments, it will be appreciated that various changesor modifications may be made without departing from the scope of theinvention as defined in the appended claims.

1-15. (canceled)
 16. A guide assembly for a disc brake, the guideassembly comprising: a disc brake caliper having a bore for receiving aguide pin, wherein the bore has a substantially circular cross-sectionalprofile; and a guide bush member mounted in the bore, the guide bushmember being a strip of metal formed into a tube having a substantiallycircular cross-sectional profile, and including first and second thinnedstrip regions arranged on opposing sides of an inner face of the guidebush member.
 17. The guide assembly of claim 16 wherein the first andsecond thinned strip regions are spaced apart from each other.
 18. Theguide assembly of claim 16 wherein the first and second thinned stripregions are predetermined locations of the strip that have been broachedor machined to be thinner with respect to a remainder of the strip. 19.The guide assembly of claim 16 wherein the first and second thinnedstrip regions are arranged in a circumferential direction.
 20. The guideassembly of claim 16 wherein the guide bush member includes third andfourth sliding strip regions on opposing sides of the inner face of theguide bush member, wherein the third and fourth sliding strip regionsextend radially inward further than the first and second thinned stripregions.
 21. The guide assembly of claim 20 wherein the third and fourthsliding strip regions are arranged in a tangential direction.
 22. Theguide assembly of claim 20 wherein the third and fourth sliding stripregions separate the first and second thinned strip regions from eachother.
 23. The guide assembly of claim 20 wherein the third and fourthsliding strip regions have recesses.
 24. The guide assembly of claim 23wherein the recesses are disposed between and spaced apart from thefirst and second thinned strip regions and extend radially outward froman inside surface of the guide bush member toward an outsidecircumference of the guide bush member.
 25. A disc brake comprising: adisc brake caliper having a bore, wherein the bore has a substantiallycircular cross-sectional profile; a guide bush member mounted in thebore, the guide bush member being a strip of metal formed into a tubehaving a substantially circular cross-sectional profile, and includingfirst and second thinned strip regions arranged on opposing sides of aninner face of the guide bush member; and a disc brake carrier that has aguide pin arranged to be received in the guide bush member.
 26. A methodof forming a guide bush member for receiving a guide pin of a discbrake, the method comprising: providing a strip of metal; broaching ormachining two portions of the strip so as to thin the two portions withrespect to a remainder of the strip; and forming the strip into a tubewith a substantially circular cross-sectional profile such that the twoportions are located on opposing inner faces of the tube.
 27. The methodof claim 26 further comprising inserting the guide bush member into abore disposed in a disc brake caliper of the disc brake, wherein thebore has a substantially circular cross-sectional profile.
 28. Themethod of claim 27 wherein inserting of the guide bush member includesinserting the guide bush member into the bore such that the two portionsare arranged in a circumferential direction.